Alloy steel



Feb. 25, 1947.

Filed March 4, 1942 I.; G. SELMI ET AI.

ALLOY STEEL 4 she'ets-sheet `1 FROM END IN I6 OF AN INCH FIGI.

`EN1OR. LUCIANO G. SIEQIXAI and CLARENCE L. ALTENBURGER MyW-DM .ATTORN EYS- G. sELMlA ET Al. l2,416,648

ALLOY STEEL Feb. 25, `1947.

4 Sheets-Sheet 2 Filed March 4, 1942 PERCENTAGE OF MOLYBDENUM INVENT OR. LUCIANO G. SELMI dnd l f CLARENCE L,AI TENBURGER $1/ ,a/aluM/f AT ,TO RMEXS.

FIG.2.

Feb. 25, 1947. G, sELMl ETAL 2,416,648

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A TTORNEY Patented Feb. 25, ,-19471- Y ALLOY STEEL Luciano-G. S'el'mi; Detroit, and Clarence ltliltenburger,` Dearborn, Mich.,.l assignorsA to Great; Lakesv Steelsv Corporation, Ecorse, Miclfi., l a `cor-v` poration of Delaware 12 crane-..5 1. y V This invention relates to=linprovements in low alloy; high tensile steels which are adapted to be' he'attreatedi Examples of such steels have beendescribed'.v

in our United States Patents Nos. 2,234,130,A now Reissue No. 22,072, and 2,250,505, andour. colpending application, Serial No; 403,188, ledJul'y y ff Aissue patent above mentionedg teaches varying the molybdenumv content: The application gives hardness tables of steels. designated, X-Y---Z showing varying silicon; and manganese, and vfollowing these tables weA speak of varying themanganese content up to 1.00%.. According to` our present discovery there is a deiiniterrelationf ship for a most effective andy economical use of molybdenum in amounts having a relation to the other elements, lparticularly'l manganese as hereinafter appears. y

The' general increasing'desire and demands for substitutions of low alloys for even'wider` uses than heretofore contemplated have prompted further'investigation and' researches for steels of the nature of those. set forth in our above identiii'ed' patents' and We have found we may attain additional desirable characteristics and improved particularly hardenabilit'y values in'r'elation to molybdenum andother alloy contents.

The sizeof sectilin-y in; which this maximum hardness; or sorne'otherlower 'hardnesslwhi'ch might arbitrarily be selected; may.:v be attained throughout, depends upon hardenability which visafunction and an effect of the amounts, na-

ture.y andi ratios of Varying alloying elements.

The'present application teaches specificallythe i provision of a Widely useful steel in which alloy'- ing elements of great importance in the war program, such as chromium, silicon, manganese and molybdenum, are used in minimum quantities.

B`y the present invention we may use molybdenuin` more effectively and economically. We

attain exceptional harden'ability or depthl hardening capacity andv adaptability for case carburizing, giving a case structure showing a virtual lack of cementitic' membranes. v

In our first mentioned patent is described an analysis with loW molybdenum content and which fof. the present invention havingl varying vfigure.

This application is particularly concerned withv ourdiscovery that in an alloy of this type'a certain proportionate amountv of' molybdenum added for heat treating purposes has@ a critical upper limit" andA practicallowen'limit More' molybe denurn may increase vthe overall hardness ofv the alloy as'rolled or slow cooledbutjit doesV notadj vantageously increase the har-denabil-ity or depth hardening clfiaracteristicsV obtained in heat' treat.-

ing. Y .v V

For convenient' illustration and comparison of the effects of modicationof chemistry, `physical properties and characteristics, reference may `be had to the accompanying drawings-infwhich-a f Fig. y1;.is a chart showing the vheat treating characteristics of specificV examples of theV` alloy 'pro-` portions ofmolydenum, and Y Fig. 2 is a chart diagrammatically illustrating the rateofA change of hardness of the alloywlth increasing amounts of; molydenum.

Fig. 3 is; a microphotograph showing the structure of such a steel, magnification being approximately m and taken of a sample having,V the chemical ailoying Fig. 4v is a chart showing physical properties'.` .y Referringv more particularlyjtoEig'. 1, itwil1be apparent that with increasing. amounts' ofinciy lybdenum,. the hardenability" of the al1oy'.in

creases proportionally upto about' .1'5% mol'ylo-s` denum, Vafter which the increase in hardenability for' added"V increasements" of' molybdenumrf'alls off rapidly. The curve of Fig. 2 was plotted 'from' values; representing thecurvature of the curves atfthe. depth of twenty-sixteenths, as shownand these. values Were determined in the manner defscribedon pages 76 and 77 Loves Dilferential and Integral Calculus published in 1918.

It will be apparent from an inspection ofFig.-2

that, the optimum needed percentage of` molyb-F Adenumis about .15% in the low carbonLv ranges herein given. In practice, however, due tothe presence of varying amounts of molybdenum in the scrap used and other factors beyond the control of the operator, it is impractical .to come closer than about .05% either side of the desired proportion. Since, as shown. in Fig. 2, thehard enability changes Very rapidly below:V .10% molybdenum, a proportion finally arrivedfat in they finished steel with ay content appreciably below .10% would result inv avery much-de'- creased hardenablity. On the` other hand, since the curve of Fig; 2' is relatively `fiat between' .110%1 elements tabulated belovsrK this and. 20%. molybdenum, it is advisable to arrive at a ,iinished-y steel having a molybdenum content within this range.Y 'With overv .20%'mo'lybdenum it is apparent that there is little changein hard-` enability. Thus we nd a critical upper limit to 'j' the amount which would be used Where the heat Y treating characteristics of the steel are controlling Withinthe limits given in' the examples for the amounts of other elements, particularly manganese. The Ylower practical limit of .10% and the upper critical limit of .20% molybdenum would normally, in practice, teach anaddition of` y molybdenum such as to` arrive at .15% in the the steel maker would normally vary the resulting vproportion of molybdenum in the nished steel somewherebetween .10% and .20%.

.f .',With manganese .75% to .80% any increase in HARDENABILITY TABLE linished steel. Conditions beyond the control of I A steel of this specific analysis is especially desirable where objects diflicultv to cold form are to be made and heat treated to derlnitel physical properties. The hardenability of the steel, as to tion of an example of our steeLcontaining .16% carbon, .74% manganese, .85% silicon .59% chromium, .15% molybdenum, .16% zirconium,

.018% sulphur, and .029% phosphorus are attained, were shown in Fig. 1 of our Patent No.

2,234,130. rCompare the; values on Chart Fig. 4

noting the molybdenum .15%.. f Thehardenability of examples of steels of the present invention is indicated in the table-below;V

PLAIN END QUNCH BAR Tnsr 1" DIAMETER X 3" LONG Rockwell vC hardness j -Distance, 16ths X-15 X-20 X-25 Fine Fine Fine Fine Fine Fine Fine Fine Fine Fine 1,v 630 l, 630 1, (iZlv 1, 700 l, 700 1, 700 1, 700 1, 600 l, 700 l, 625 .15 .16 .19 .19 .22 .22 .23 .24 y .23 e .74 .68 .77 .72 .67 .6l .79 Q81 .75

. O18 023 019 018 020 018 015 020 018 .85 .80 .90 y .96 .79 .63 .64 .94 '.99 .59 .52 .60 .63 .63 .62 .66 .59 .64 .l5 .O9 .08 .18 .17 .21 .14 .17 '.15 .16 .14 ,13 .16 .11 ..11 .12 .19 .17

molybdenum over '.15% does not contribute materially to the hardenability of the alloy. However, if the manganese be increased to .85% to .95%fa material increase in hardenability is obtained by changing the molybdenum content from..15% -to .20%.

The steel of the present invention, in addition to iron and incidental impurities, preferably con# tains the Vfollowingelements within the ranges specii'led: i

I 'Y Per cent e Carbon Y .0G-.24 I Manganesev l i .S0-.75 Silicon .60-.90 4Chromium .30-.75 Molybdenum -..Y v .l0-.20 Zirconium .l0-.20 .1

4 .o5-Max. Phosphorus r; Y j .Clit-Max.

A typical alloy within the foregoing range will contain: j Per cent Carbon Manganese s f Molybdenum ;A-- Y Zirconium .A p ..141 SulphurV .023

From the `foregoing table, it. willbe apparent that the hardenability of our steels compare very favorably with knownV and widelyv used steels of higher amounts of alloying elements, forexample, our steel designated atthe ltop of the column, X-20 compares favorably with well-known higher chrome steel SAE-4120 similarly, our steels listed under the columns headed X-25may be compared favorably to the highcontentlnickel steelsV knownA asSAE-4820 in v'respect to the hardenability. f

It is apparent, Yby comparison of our present steel Awith the properties, including the hardenf ability of standard widely used steels having like properties and characteristics, that marked and important savings of strategic and valuable alloying velements may be effected, while the,V very desirable objectives ofA steels having Vthese iin-.- proved characteristics may be attained without special treatment or'equipment.r

VAs previously mentionedthe steels are well lack of cementiticV membranes,Fig. 3 showing the micrographic structures of a carburized case of a steel of the analysis indicated. Steels of the present invention are particularly vadapted for manufacture into special articles,

such, for example, as oxygen supply cylinders,

bombs, airplanewheels, rivets, army. helmets,

Likewise, and by reason of the same properties and characteristics attained, steels made according to our present invention are suitable for a wide variety of civilian uses such as automobile and truck gears.

Having thus described our invention, the nature and scope thereof are defined in the appended claim, it being understood that the particular relationships and ranges specied may be subject to slight or reasonable variations without departing from the spirit of our invention.

We claim:

A carburized steel article containing as essential alloying elements about 0.5 to about .75 per cent of chromium, about 0.6 to about 0.9 per cent of silicon, about 0.1 to about 0.2 per cent of molybdenum, .10 to .20 per cent of zirconium, carbon from 0.1 to about 0.24 per cent and in an amount such that the steel is hardenable by heat treatment, and the remainder iron together with impurities and elements in amounts which do not adversely affect thel carburizing and heat treating characteristics of the steel, and characterized by a carburized case resistant to spalling and low in or substantially free from massive carbides, and high tensile strength in the core as the result of heat treatment.

LUCIANO G. SELMI.

CLARENCE L. ALTENBURGER.

REFERENCES CITED The following references are of record in the le of this patent: l

UNITED STATES PATENTSVv Number Name Date 1,278,082 Wills Sept. 3, 1918 2,250,505 selmi July 29, 1941 2,234,130 Selmi Mar. 4, 1941 

